— We did not see him at the lecture yesterday．

— You _______ him, since I went to an international conference with him．

A．mustn’t have seen

B．can’t have seen

C．couldn’t see

D．needn’t have seen

根据冲刷及地基承载能力确定墩台基础的安全埋置深度，安全埋置深度越深越好。